Thermal sensor

ABSTRACT

A method of calibrating a thermal sensor device is provided. The method includes extracting an incremental voltage to temperature curve for a diode array from a first incremental voltage of the diode array at a first temperature. The diode array and a device under test (DUT) which includes a thermal sensor are heated. After heating the diode array, a first incremental temperature is determined from the incremental voltage to temperature curve for the diode array and a second incremental voltage of the diode array after heating the diode array. An incremental voltage to temperature curve is extracted for the DUT from the first incremental temperature, a first incremental voltage for the DUT at the first temperature, and a second incremental voltage of the DUT after heating the device under test. A temperature error for the thermal sensor is determined from the incremental voltage to temperature curve for the DUT.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/238,762 filed Apr. 23, 2021, now U.S. patent Ser. No. 11/448,691 thedisclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

The semiconductor industry has experienced rapid growth due toimprovements in the integration density of a variety of electroniccomponents, such as transistors, diodes, resistors, capacitors, etc.This improvement in integration density has come from shrinking thesemiconductor process node. As device dimensions shrink, voltage nodesalso shrink, with core device voltages trending toward less than 1 Volt,and input/output (I/O) device voltages under 2 Volts. Temperaturevariation of device, such as transistor threshold voltage, is a concernas voltage nodes shrink. Temperature variation of device parameters,such as transistor threshold voltage, is a concern as voltage nodesshrink. For example, transistor threshold voltage may vary on the orderof single millivolts per degree Celsius. Integrated circuits (ICs) areexpected to operate in large temperature ranges, which correspond tolarge temperature variations that may be on the same order of magnitudeas the device parameter. Therefore, characterization of circuitperformance for temperature variation is increasingly important.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion. In addition, the drawings are illustrative as examples ofembodiments of the invention and are not intended to be limiting.

FIG. 1 is a diagram of an example test system in accordance with someembodiments.

FIG. 2A is a diagram of an example diode in accordance with someembodiments.

FIG. 2B is a diagram of another example diode in accordance with someembodiments.

FIG. 3 is diagram illustrating example placement of elements of testsystem in accordance with some embodiments.

FIG. 4 illustrates a process flow for the method for calibrating a testsystem in accordance with some embodiments.

FIG. 5 illustrates an example graph illustrating AV-to-T curves of thetest system in accordance with some embodiments.

FIG. 6 is a block diagram illustrating an example of a processing systemin accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Integrated Circuit (IC) performance is typically characterized forprocess, voltage, and temperature variation. Temperature variationcharacterization is generally performed by attaching a wafer to athermal chuck, which heats and/or cools the wafer to specifictemperatures for circuit performance characterization. Absolutetemperature of the wafer heated by the thermal chuck is not perfectlyuniform. For example, the thermal chuck may be set to heat the wafer to50° C., but the wafer may have regions with temperatures ranging from46° C. to 50° C. Thus, a temperature profile of the thermal chuck istypically obtained through use of a thermocouple prior to testing thewafer for circuit performance under temperature variation. Thetemperature profile may be obtained by heating/cooling the wafer tovarious temperatures (e.g., —25° C., 0° C., 25° C., 50° C., and 70° C.),allowing temperature of the wafer to stabilize for 30 minutes to onehour, then obtaining a number of temperature data points at positionsdistributed over the surface of the wafer. For example, five data pointsspread over the surface of the wafer may be obtained for eachtemperature.

Many problems arise when using the thermal profile obtained through theaforementioned process. For example, the thermal couple is not able toprovide an accurate reading of the temperatures at the various datapoints. Moreover, during test, the wafer temperature is allowed tostabilize for 30 minutes to one hour before circuit performance at thetest temperature can be characterized. This greatly inhibits throughput,as each test temperature requires the stabilization period, and anywherefrom 5 to 8 (or more) test temperatures may be characterized. Inaddition, probe pitches change at different temperatures resulting inbad contact issues. Finally, distance from a temperature sensitivecircuit under test to the nearest available data point on the thermalprofile may be large, such that absolute temperature at the location ofthe circuit under test is hard to determine with any confidence.

The disclosure provides an improved test system and method tocharacterize a temperature accuracy of a thermal sensor of the testsystem at the room temperature. More specifically, the disclosureprovides techniques for calibrating a thermal sensor of the test system.Through use of a diode array and a metal heater, temperaturecharacteristics of the thermal sensor is monitored through a roomtemperature test. The disclosure further provides faster temperaturesettings without lifting a probe of the test system. In the disclosedtechniques, temperature changing or temperature setting equipments maynot be required. In addition, there is lesser probe contact time andeasier for rechecking abnormal dies with flexibility of re-testing.

FIG. 1 is a diagram illustrating a wafer testing system 100 (simplyreferred to as a test system 100) in accordance with some embodiments.Test system 100 can be used to determine thermal characteristics of anintegrated circuit or a portion of an integrated circuit at differenttemperatures. In some examples, test system 100 can be used to calibratea thermal sensor being used to determine the thermal characteristics ofan integrated circuit. As shown in FIG. 1 , test system 100 includes awafer 102, a probe 104, a current source 106, a voltage detector 108, aheater 114, a diode array 112, and a device under test 110.

Wafer 102 includes multiple integrated circuit dies 116 (or simply “dies116”). Dies 116 are formed in and on the semiconductor wafer 102, andmay include active circuits, passive circuits, and interconnectstructures. A number of dies 116 in wafer 102 may depend on dimensionsof each die 116 and wafer 102. In some examples, wafer 102 includeshorizontal scribe lines and vertical scribe lines (not shown) which runbetween rows and columns of dies 116, respectively, and serve multiplepurposes in fabrication of dies 116. For example, the scribe linesphysically isolate individual dies 116 from each other, and provide aguideline for a diamond saw during singulation. Prior to singulation,the scribe lines may also be used for placement of test circuits fortesting electrical and functional characteristics of the dies 116.

In some examples, each die 116 of wafer 102 may include a temperaturesensing circuit 118 (also referred to as a temperature sensor 118 or athermal sensor 118). Thermal sensor 118 can include a temperaturesensing device, such as a temperature sensitive diode (also referred toas a thermal diode) formed integrally in wafer 102. In some examples,the temperature sensitive diode is formed at the same time as thecircuits in dies 116 as part of the circuit fabrication process, or itcan be formed in a separate fabrication process. The temperaturesensitive diode operates such that, during operation, as it conductscurrent, a voltage drop across it varies with temperature in a known andcharacterized fashion. Hence, a measurement of the voltage drop acrossthe temperature sensitive diode can be used to determine a currenttemperature of wafer 102.

Probe 104 is used to electrically test circuits on wafer 102 and isexternal to wafer 102. In some examples, probe 104 includes a probe headwhich is positioned such that a group of probers of probe 104 arebrought into contact with predetermined contact points (for example,input terminals of temperature sensitive diodes), on individual circuitsformed in die 116 of wafer 102. Probe 104 in conjugation with currentsource 106 and voltage detector 108 applies predetermined excitations tothe predetermined contact points of die 116 and sense responses to theexcitations. In some examples, thermal sensor 118 can be located inprobe 104. In such examples, probe 104 determines a current temperatureof wafer 102 through thermal sensor 118. In some examples, probe 104 mayinclude a memory to store instructions and data, and a processor coupledto the memory and configured to execute the instructions stored on thememory.

Current source 106 is a direct current (DC) supply. In some examples,current source 106 is capable of providing at least two differentcurrents, that is, a first current and a second current. In someexamples, current source 106 provides the first current and thenprovides the second current. For example, current source 106 providesthe first current, then after a predetermined time, provides the secondcurrent which is a multiple of the first current (for example, twice thefirst current). In some examples, the second current may be any multipleof the first current, and is not limited to integer multiples. And, theorder of inputting the first current and the second current may bereversed. In some examples, current source 106 provides the firstcurrent and the second current to die 116 of wafer 102. For example,current source 106 provides the first current and the second current todie 116 of wafer 102 through one or more current pads associated withdie 116. In some other examples, current source 106 provides the firstcurrent and the second current to die 116 of wafer 102 through probe104.

Voltage detector 108 senses the voltage response of die 116 duringtesting. In some examples, voltage detector 108 draws little to nocurrent when measuring the voltage response, so as not to affect currentflow set up by current source 106. Voltage detector 108 detects a firstvoltage (e.g., V₁) while the first current is inputted by current source106, and further detects a second voltage (e.g., V₂) while the secondcurrent is inputted by current source 106. Then, an incremental voltage(ΔV) can be calculated as V₂−V₁. In some examples, voltage detector 108determines the incremental voltage (ΔV) as V₂−V₁. In some examples,voltage detector 108 senses the first voltage and the second voltagefrom die 116 of wafer 102 through one or more voltage pads associatedwith die 116. In some other examples, voltage detector 108 senses thefirst voltage and the second voltage from die 116 of wafer 102 throughprobe 104.

Device under test 110 (also referred to as DUT 110) is a selected die116 of wafer 102. In some examples, die 116 is randomly selected fromwafer 102. In some example, some dies 116 of wafer 102 are pre-marked tobe used during testing of wafer 102. In some other examples, apredetermined number of dies 116 of wafer 102 are selected (for example,randomly selected one fourth of total number of dies 116). In otherexamples, every die 116 of wafer 102 is selected.

Diode array 112 includes an array of a plurality of diodes. In someexamples, diode array 112 includes an array of a predetermined number ofdeep n-well (DNW) diodes. FIG. 2A illustrates an example DNW diode 200of diode array 112 in accordance with some embodiments. As shown in FIG.2A, an example diode 200 of diode array 112 includes a p-substrate 204with a deep n-well (DNW) 202 channel formed in p-substrate 204. Thus,DNW diode 200 is formed between p-substrate 204 and DNW 202 channel.

In some examples, diode array 112 includes an array of a predeterminednumber of a bipolar junction transistors (BJTs) in diode connectedconfiguration. FIG. 2B illustrates another example diode 250 which is aBJT in diode connected configuration in accordance with someembodiments. As shown in FIG. 2B, diode 250 includes a p-substrate 204with a DNW 202 channel formed in p-substrate 204. In addition, a p-well(PW) 206 channel is formed in DNW 202 channel. Thus, DNW diode 250 isformed between PW 206 channel and DNW 202 channel.

In some examples, diode array 112 provides a well-defined relationshipbetween an incremental voltage (ΔV) and temperature (T). For example, atemperature dependence relationship of diode array 112 and temperatureis provided by the following equation:

$\begin{matrix}{{\Delta V_{BE}} = {\frac{KT}{q} \times {\ln\left( \frac{I_{C1}}{I_{C2}} \right)}}} & (1)\end{matrix}$where ΔV_(BE) is an incremental bandgap voltage of diode array 112, K isBoltman's constant, T is temperature in Kelvins, q is charge on anelectron, and I_(c1) and I_(c2) are two different currents. Solving fortemperature, the following equation is obtained from equation (1):

$\begin{matrix}{T = \frac{\Delta V_{BE} \times q}{K{\ln(N)}}} & (2)\end{matrix}$where N is a ratio of I_(c1) to I_(c2).

Thus, diode array 112 provides a near ideal linearity with anintersection at 0° K and a negligible temperature error. Therefore, anincremental voltage to temperature (that is, ΔV to T) curve is obtainedfor diode array 112 by room-temperature measurements of the incrementalvoltage (ΔV) and the temperature (T). In some examples, die-to-dievariations in the temperature is eliminated by increasing diode area.For example, diode area is increased to 50GPX50GP where GP is a gatepitch to eliminate die-to-die variations in the temperature.

Heater 114, also referred to as a temperature control system, providesheating to device under test 110 and diode array 112. That is, heater114 can raise or lower a temperature of both DUT 110 and diode array112. For example, heater 114 is placed in proximity of device under test110 and diode array 110.

FIG. 3 illustrates an example placement 300 of device under test 110,diode array 112, and heater 114. As shown in FIG. 3 , heater 114 isplaced between device under test 110 and diode array 112. Thus, heater114 provides an uniform heating of both device under test 110 and diodearray 112. A heater current source I_(h) 106 is connected to heater 114.For example, heater current source I_(h) 106 is connected to a firstterminal of heater 114 and a second terminal of heater 114 is connectedto ground.

As shown in FIG. 3 , heater 114 includes a plurality of connected metalstrips which generate heat when heater current source I_(h) 106 ispassed through it. In some examples, an amount of heat generated byheater 114 is controlled by controlling an amount of current provided toheater 114 by heater current source I_(h) 106. Hence, heater currentsource I_(h) 106 is increased to increase the amount of heat produced byheater 114 and is decreased to decrease the amount of heat produced byheater 114. In some examples, increasing the amount of heat produce byheater 114 increases a temperature of both device under test 110 anddiode array 112. Similarly, decreasing the amount of heat produced byheater 114 decreases a temperature of both device under test 110 anddiode array 112. Therefore, a temperature of both device under test 110and diode array 112 is changed by varying heater current source In 106.In some examples, an area of heater 114 is greater than an area of diodearray 112 which is greater than an area of device under test 110. Anumber of metal strips and a dimension of each metal strips of heater114 is configurable.

In example embodiments, both device under test 110 and diode array 112can be heated to a temperature of greater than 300° C. which covers athermal sensor usage range. In addition, heater 114 provides a uniformtemperature distribution in a heating region because it contains aplurality of metal plates which have a good thermal conductance. In someexamples, heater 114 is an on-die metal heater. In some other examples,heater 114 is formed using MD or gate resistors on diode array 112.Heater 114 has electromagnetic tolerance for a current of greater than2000 mA.

FIG. 4 is a flow diagram of a method 400 for calibrating a thermalsensor 118 used for determining thermal characteristics of an integratedcircuit in accordance with some embodiments. Method 400 is described interms of test system 100 shown in FIGS. 1-3 . The calibration processmay be used to determine a temperature error of thermal sensor 118 andhence provide a more accurate measurement of a current temperature ofdevice under test 110. In some examples, method 400 can be performed byprobe 104. In some other examples, method 400 can be performed by aprocessing system described with reference to FIG. 6 of the disclosure.In other examples, method 400 can be stored as instructions in a storagedevice accessible to a processor. The stored instructions can beexecuted by the processor to perform method 400. The storage device tostore the instructions can include a non-transitory computer readablemedium.

At block 410 of method 400, a first incremental voltage (ΔV1_(DNW_J))for a diode array is determined at a first temperature (T1). Forexample, the ΔV1_(DNW_J) for diode array 112 is determined at a roomtemperature. The ΔV1_(DNW_J) for diode array 112 at the room temperaturecan be determined by applying the first current and the second currentby current source 106 and determining the ΔV1_(DNW_J) by voltagedetector 108 as a response to the first current and the second current.

For example, a first current is inputted to diode array 112. The firstcurrent may be inputted by current source 106. The first currentinjection may be controlled by an operator, and/or by automatic testequipment including current source 106 and a controller, for example.The first current inputted in diode array 112 may be on the order ofmicroamperes, such as in a range of about 2 microamperes to 20microamperes. Other ranges for the first current are also contemplatedherein.

The first current injected by current source 106 sets up a first voltageacross diode array 112, and the first voltage is measured as the firstcurrent is flowing through diode array 112. The first voltage may beread by voltage detector 108. The first current may be allowed tostabilize before the first voltage is read. The first voltage read outby voltage detector 108 may be stored.

After reading the first voltage, a second current is inputted to diodearray 112 by current source 106. In some examples, the first current maybe turned off prior to inputting the second current. The second currentmay be inputted to diode array 112 by current source 106. The secondcurrent may be a multiple of the first current, or the second currentmay be a fraction of the first current. Magnitude of the second currentmay be on the order of microamperes, such as in a range of about 2microamperes to about 20 microamperes, for example. Other ranges for thesecond current are also contemplated herein. In some examples, a ratioof the second current to the first current may be 1/10, 1/2, 2, 10, orthe like.

While keeping the second current flowing through diode array 112, asecond voltage of the diode array 112 may be measured by voltagedetector 108. The second current injected by current source 106 sets upthe second voltage across diode array 112. The second voltage may beread by voltage detector 108. The second current may be allowed tostabilize before the second voltage is read. The second voltage read outby voltage detector 108 may be stored. Then a difference between thesecond voltage corresponding to the second current and the first voltagecorresponding to the first current is determined to determine theΔV1_(DNW_J) for diode array 112.

At block 415 of method 400, a first incremental voltage (ΔV1_(DUT)) fora device under test is determined at a first temperature (T1). Forexample, the ΔV1_(DUT) for device under test 110 is determined at a roomtemperature. The ΔV1_(DUT) for device under test 110 at the roomtemperature can be determined by applying the first current and thesecond current by current source 106 and determining the ΔV1_(DUT) byvoltage detector 108 as a response to the first current and the secondcurrent.

At block 420 of method 400, a linear diode array ΔV-to-T curve isextracted from the first incremental voltage (ΔV1_(DNW_J)) and the firsttemperature (T1) for the diode array 112. For example, the ΔV1_(DNW_J)and T1 can be plotted on a graph having an incremental voltage axis(that is, ΔV axis) and a temperature axis (that is, T axis). FIG. 5illustrates a graph 500 having ΔV axis and a T axis. For example, and asshown in FIG. 5 , graph 500 includes ΔV axis 516 and a T axis 518. Afirst point 506 representing (ΔV1_(DNW_J), T1) of diode array 112 isplotted in graph 500. First point 506 is then connected with originpoint 520 representing (0,0) of graph 500 to extract linear diode arrayΔV-to-T curve 502. In addition, and as shown in graph 500, a secondpoint 508 representing (ΔV1_(DUT), T1) of device under test 110 is alsoplotted in graph 500.

At block 425 of method 400, a first slope (S_(DNW_J)) for the diodearray ΔV-to-T curve is determined. For example, the first slope(S_(DNW_J)) for diode array ΔV-to-T curve 502 is determined. In someexamples, the first slope (S_(DNW_J)) is determined by dividing adifference in the y-coordinates of first point 506 representing(ΔV1_(DNW_J), T1) and origin 520 representing (0,0) of diode arrayΔV-to-T curve 502 by a difference in the x-coordinates of first point506 representing (ΔV1_(DNW_J), T1) and origin 520 representing (0,0). Insome examples, origin 520 is an intersection point of the incrementalvoltage axis (that is, ΔV axis 516) and the temperature axis (that is, Taxis 518).

At block 430 of method 400, heater power is raised, for example, to P₀.In some examples, the power of heater 114 is raised to P0 by raising aheater current I_(h). Raising the heater current I_(h) increases anamount of heat being generated by heater 114. This leads to increase inthe temperature of both device under test 110 and diode array 112. Forexample, the temperature of both device under test 110 and diode array112 may increase to a second temperature T2 from the first temperatureT1. In some examples, the heater current I_(h) is increased by apredetermined amount.

At block 435 of method 400, a second incremental voltage (ΔV2_(DNW_J))for the diode array 112 is determined after heating diode array 112. Forexample, the ΔV2_(DNW_J) for diode array 112 after heating can bedetermined by applying the first current and the second current bycurrent source 106 and determining the ΔV2_(DNW_J) by voltage detector108 as a response to the first current and the second current. In someexamples, a temperature of diode array 112 may be allowed to stabilizebefore the ΔV2_(DNW_J) is determined.

At block 440 of method 400, a first incremental temperature (ΔT₀) isdetermined from diode array ΔV-to-T curve 502 and the first slope(S_(DNW_J)) based on the ΔV2_(DNW_J). For example, from the first slope(S_(DNW_J)) and the ΔV2_(DNW_J), the second temperature (T2) isdetermined. A third point 510 representing (ΔV2_(DNW_J), T2) is thenplotted in graph 500 and diode array ΔV-to-T curve 502 is extended fromfirst point 506 representing (ΔV1_(DNW_J), T1) to third point 510representing (ΔV2_(DNW_J), T2). The incremental temperature (ΔT₀) isextracted using extended diode array ΔV-to-T curve 502.

At block 445 of method 400, a second incremental voltage (ΔV2_(DUT)) fordevice under test 110 is determined after heating device under test 110.For example, the ΔV2_(DUT) for device under test 110 is determined byapplying the first current and the second current by current source 106and determining the ΔV2_(DUT) by voltage detector 108 as a response tothe first current and the second current.

At block 450 of method 400, linear device under test ΔV-to-T curve 504is extracted and a second slope (S_(DUT)) for device under test 110 isdetermined from the first incremental temperature (ΔT₀) and theΔV2_(DUT). For example, a fourth point 512 representing (ΔV2_(DUT), T2)is plotted on graph 500. Fourth point 512 representing (ΔV2_(DUT), T2)is joined with second point 508 representing (ΔV1_(DUT), T1) using astraight line to extract linear device under test ΔV-to-T curve 504.Then the second slope (S_(DUT)) for the extract linear device under testΔV-to-T curve 504 is determined. In some examples, the second slope(Spur) is determined by dividing a difference in the y-coordinates offourth point 512 representing (ΔV2_(DUT), T2) and second point 508representing (ΔV1_(DUT), T1) of device under test ΔV-to-T curve 504 by adifference in the x-coordinates of fourth point 512 representing(ΔV2_(DUT), T2) and second point 508 representing (ΔV1_(DUT), T1).

At block 455 of method 400, the heater power is changed again, forexample, to P_(i). In some examples, the power of heater 114 is changedto P_(i) by changing the heater current I_(h). Changing the heatercurrent I_(h) changes an amount of heat being generated by heater 114.This leads to change in a temperature of both device under test 110 anddiode array 112. For example, the temperature of both device under test110 and diode array 112 may change to an ith temperature (T_(i)) from aprevious temperature (for example, the second temperature (T2)). In someexamples, the heater current I_(h) is changed by a predetermined amount.

At block 460 of method 400, an ith temperature (T_(i)) is determinedfrom the device under test ΔV-to-T curve and the second slope (S_(DUT))after changing the heater power to P_(i). For example, after changingheater 114 power to P_(i), an ith incremental voltage (ΔVi_(DUT)) isdetermined by applying the first current and the second current bycurrent source 106 and determining the ΔVi_(DUT) by voltage detector 108as a response to the first current and the second current. Then, fromthe second slope (S_(DUT)) and the ΔVi_(DUT), the ith temperature (Ti)is determined. In some examples, a fifth point 514 representing(ΔVi_(DUT), Ti) may be plotted in graph 500.

At block 465 of method 400, thermal sensor temperature error (Terr) isdetermined from the ith temperature (T_(i)). For example, a differencebetween the ith temperature (T_(i)) determined from the device undertest ΔV-to-T curve 504 and the second slope (S_(DUT)), and a temperatureprovided thermal sensor 118 is determined to determine the thermalsensor temperature error (Terr). In some examples, the thermal sensortemperature error (Terr) can be determined for a multiple heatersettings. The thermal sensor temperature error (Terr) may not belinearly correlated over temperature. Therefore, calibration parameters,that is, the thermal sensor temperature error (Terr), correlating theΔVi_(DUT) to temperature may be stored in a lookup table, or acalibration equation may be derived so that the temperature readingoutputted by thermal sensor 118 may be calibrated on the fly.

FIG. 6 is a block diagram illustrating an example of a processing system600 in accordance with some embodiments disclosed herein. Processingsystem 600 may be used to calibrate a thermal sensor device used fordetermining thermal characteristics of an integrated circuit inaccordance with various processes discussed herein. Processing system600 includes a processing unit 610, such as a desktop computer, aworkstation, a laptop computer, a dedicated unit customized for aparticular application, a smart phone or tablet, etc. Processing system600 may be equipped with a display 614 and one or more input/outputdevices 612, such as a mouse, a keyboard, touchscreen, printer, etc.Processing unit 610 also includes a central processing unit (CPU) 620,storage device 622, a mass storage device 624, a video adapter 626, andan I/O interface 628 connected to a bus 630.

The bus 630 may be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, or videobus. CPU 620 may comprise any type of electronic data processor, andstorage device 622 may comprise any type of system memory, such asstatic random access memory (SRAM), dynamic random access memory (DRAM),or read-only memory (ROM).

Mass storage device 624 may comprise any type of storage deviceconfigured to store data, programs, and other information and to makethe data, programs, and other information accessible via bus 630. Massstorage device 624 may comprise, for example, one or more of a hard diskdrive, a magnetic disk drive, an optical disk drive, flash memory, orthe like.

The term computer readable media as used herein may include computerstorage media such as the system memory and storage devices mentionedabove. Computer storage media may include volatile and nonvolatile,removable and non-removable media implemented in any method ortechnology for storage of information, such as computer readableinstructions, data structures, or program modules. Storage device 622and mass storage device 624 are computer storage media examples (e.g.,memory storage).

Computer storage media may include RAM, ROM, electrically erasableread-only memory (EEPROM), flash memory or other memory technology,CD-ROM, digital versatile disks (DVD) or other optical storage, magneticcassettes, magnetic tape, magnetic disk storage or other magneticstorage devices, or any other article of manufacture which can be usedto store information and which can be accessed by processing device 600.Any such computer storage media may be part of processing device 600.Computer storage media does not include a carrier wave or otherpropagated or modulated data signal.

Communication media may be embodied by computer readable instructions,data structures, program modules, or other data in a modulated datasignal, such as a carrier wave or other transport mechanism, andincludes any information delivery media. The term “modulated datasignal” may describe a signal that has one or more characteristics setor changed in such a manner as to encode information in the signal. Byway of example, and not limitation, communication media may includewired media such as a wired network or direct-wired connection, andwireless media such as acoustic, radio frequency (RF), infrared, andother wireless media.

Video adapter 626 and I/O interface 628 provide interfaces to coupleexternal input and output devices to processing unit 610. As illustratedin FIG. 6 , examples of input and output devices include display 614coupled to video adapter 626 and I/O device 612, such as a mouse,keyboard, printer, and the like, coupled to I/O interface 628. Otherdevices may be coupled to processing unit 610, and additional or fewerinterface cards may be utilized. For example, a serial interface card(not shown) may be used to provide a serial interface for a printer.Processing unit 610 also may include a network interface 640 that may bea wired link to a local area network (LAN) or a wide area network (WAN)616 and/or a wireless link.

Embodiments of processing system 600 may include other components. Forexample, processing system 600 may include power supplies, cables, amotherboard, removable storage media, cases, and the like. These othercomponents, although not shown, are considered part of processing system600.

In some examples, instructions or software code is executed by CPU 620to perform refresh operations. The instructions or the software code maybe accessed by CPU 620 via bus 630 from storage device 622, mass storagedevice 624, or the like, or remotely through network interface 640.Further, in some examples, the refresh operations instructions may bereceived though I/O interface 628 and/or stored in storage device 622 ormass storage device 624 in accordance with various methods and processesimplemented by the software code.

In accordance with example embodiments, a method of calibrating athermal sensor device, the method comprising: extracting an incrementalvoltage to temperature curve for a diode array from a first incrementalvoltage of the diode array at a first temperature; heating the diodearray and a device under test, wherein the device under test includes athermal sensor; determining, after heating the diode array, a firstincremental temperature from the incremental voltage to temperaturecurve for the diode array and a second incremental voltage of the diodearray after heating the diode array; extracting an incremental voltageto temperature curve for the device under test from the firstincremental temperature, a first incremental voltage for the deviceunder test at the first temperature, and a second incremental voltage ofthe device under test after heating the device under test; anddetermining a temperature error for the thermal sensor from theincremental voltage to temperature curve for the device under test.

In example embodiments of the disclosure, an apparatus for calibrating athermal sensor comprises: a memory device storing instructions forcalibrating a thermal sensor; and a processor connected to the memorydevice, wherein the processor is operative to execute the instructions,wherein, when executed, the instructions cause to: determine a firstincremental voltage for a diode array at a first temperature; determinea first incremental voltage for a device under test at the firsttemperature, the device under test comprising the thermal sensoroperative to determine a temperature of the device under test; determinea first slope from the first incremental voltage of the diode array;heat both the diode array and the device under test; determine a secondincremental voltage for the diode array after heating the diode array;determine a first incremental temperature based on the secondincremental voltage for the diode array and the first slope; determine asecond incremental voltage for the device under test after heating thedevice under test; determine a second slope from the second incrementalvoltage for the device under test and the first change in temperature;and determine a temperature error for the thermal sensor based on thesecond slope.

In accordance with example embodiments, a calibration system forcalibrating a thermal sensor, the calibration system comprising: a diodearray; a heater placed between the diode array and a device under test;a probe operative to: extract an incremental voltage to temperaturecurve for the diode array from a first incremental voltage of the diodearray at a first temperature; determine, after heating the diode arrayusing the heater, a first incremental temperature from the incrementalvoltage to temperature curve for the diode array and a secondincremental voltage of the diode array after heating the diode array;extract an incremental voltage to temperature curve for the device undertest from the first incremental temperature, a first incremental voltagefor the device under test at the first temperature, and a secondincremental voltage of the device under test after heating the deviceunder test; and determine a temperature error for a thermal sensor ofthe device under test from the incremental voltage to temperature curvefor the device under test.

This disclosure outlines various embodiments so that those skilled inthe art may better understand the aspects of the present disclosure.Those skilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions, and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A method of calibrating a thermal sensor device,the method comprising: extracting an incremental voltage to temperaturecurve for a diode array from a first incremental voltage of the diodearray at a first temperature; determining, after heating the diode arrayusing a heater, a first incremental temperature from the incrementalvoltage to temperature curve for the diode array and a secondincremental voltage of the diode array after heating the diode array;extracting an incremental voltage to temperature curve for a deviceunder test from the first incremental temperature, a first incrementalvoltage for the device under test at the first temperature, and a secondincremental voltage of the device under test after heating the deviceunder test; and determining a temperature error for a thermal sensor ofthe device under test from the incremental voltage to temperature curvefor the device under test.
 2. The method of claim 1, further comprising:determining the first incremental voltage of the diode array at thefirst temperature; and determining the first incremental voltage for thedevice under test at the first temperature.
 3. The method of claim 1,wherein extracting the incremental voltage to temperature curve for thediode array comprises: plotting the first incremental voltage for thediode array at the first temperature as a first point in a graphcomprising an incremental voltage axis and a temperature axis; andjoining the first point to an intersection point of the incrementalvoltage axis and the temperature axis.
 4. The method of claim 1, whereindetermining the first incremental temperature comprises: determining asecond temperature of the diode array from the second incrementalvoltage and a first slope of the incremental voltage to temperaturecurve for the diode array; and determining the first incrementaltemperature as a difference between the second temperature and the firsttemperature.
 5. The method of claim 1, wherein extracting theincremental voltage to temperature curve for the device under testcomprises: plotting the first incremental voltage for the device undertest at the first temperature as a second point in a graph comprising anincremental voltage axis and a temperature axis; plotting the secondincremental voltage for the device under test at the first incrementedtemperature as a third point in the graph; and joining the second pointand the third point.
 6. The method of claim 1, wherein determining thetemperature error for the thermal sensor comprises: determining a thirdincremental voltage for the device under test after reheating the deviceunder test; determining a third temperature of the device under testafter reheating the device under test from a second slope of theincremental voltage to temperature curve for the device under test andthe third incremental voltage of the device under test; and determininga difference between the third temperature and a temperature reading ofthe thermal sensor.
 7. The method of claim 1, wherein determining thetemperature error for the thermal sensor comprises determining thetemperature error for multiple temperatures of the device under test. 8.The method of claim 1, wherein heating the diode array and the deviceunder test comprises heating the diode array and the device under testwith a metallic heater.
 9. The method of claim 1, wherein heating thediode array and the device under test comprises heating the diode arrayand the device under test with a metallic heater, wherein the metallicheater is place between the device under test and the diode array.
 10. Acalibration system for calibrating a thermal sensor, the calibrationsystem comprising: a diode array; a heater placed between the diodearray and a device under test; a probe operative to: determine a firstincremental voltage for a diode array at a first temperature; determinea first incremental voltage for a device under test at the firsttemperature, the device under test comprising the thermal sensoroperative to determine a temperature of the device under test; determinea first slope from the first incremental voltage of the diode array;determine a second incremental voltage for the diode array after heatingthe diode array; determine a first incremental temperature based on thesecond incremental voltage for the diode array and the first slope;determine a second incremental voltage for the device under test afterheating the device under test; determine a second slope from the secondincremental voltage for the device under test and the first change intemperature; and determine a temperature error for the thermal sensorbased on the second slope.
 11. The calibration system of claim 10,wherein the probe being operative to determine the temperature error forthe thermal sensor comprises the probe being operative to: determine athird incremental voltage for the device under test after reheating thedevice under test; determine a third temperature of the device undertest after reheating the device under test from the second slope; anddetermine a difference between the third temperature and a temperaturereading of the thermal sensor.
 12. The calibration system of claim 10,wherein the probe being operative to determine the temperature error forthe thermal sensor comprises the probe being operative to determine thetemperature error for multiple temperatures of the device under test.13. The calibration system of claim 10, wherein the heater comprises ametallic heater.
 14. The calibration system of claim 10, wherein thedevice under test is a die of a wafer.
 15. An apparatus for calibratinga thermal sensor, the apparatus comprising: a memory device storinginstructions for calibrating a thermal sensor; and a processor connectedto the memory device, wherein the processor is operative to execute theinstructions, wherein, when executed, the instructions cause to: extractan incremental voltage to temperature curve for a diode array from afirst incremental voltage of the diode array at a first temperature;determine, after heating the diode array, a first incrementaltemperature from the incremental voltage to temperature curve for thediode array and a second incremental voltage of the diode array afterheating the diode array; extract an incremental voltage to temperaturecurve for a device under test from the first incremental temperature, afirst incremental voltage for the device under test at the firsttemperature, and a second incremental voltage of the device under testafter heating the device under test; and determine a temperature errorfor a thermal sensor from the incremental voltage to temperature curvefor the device under test, wherein the thermal sensor is associated withthe device under test.
 16. The apparatus of claim 15, wherein the diodearray comprising a plurality of deep n-well diodes.
 17. The apparatus ofclaim 15, wherein the device under test is a die of a wafer.
 18. Theapparatus of claim 15, wherein the instructions causing to determine thetemperature error for the thermal sensor comprises the instructionscausing to: reheat the device under test; determine a third incrementalvoltage for the device under test after reheating the device under test;determine a third temperature of the device under test after reheatingthe device under test from a second slope of the incremental voltage totemperature curve for the device under test and the third incrementalvoltage of the device under test; and determine a difference between thethird temperature and a temperature reading of the thermal sensor. 19.The apparatus of claim 15, wherein the instructions causing to extractthe incremental voltage to temperature curve for the diode arraycomprises the instructions causing to: plot the first incrementalvoltage for the diode array at the first temperature as a first point ina graph comprising an incremental voltage axis and a temperature axis;and join the first point to an intersection point of the incrementalvoltage axis and the temperature axis.
 20. The apparatus of claim 15,wherein the instructions causing to determine the first incrementaltemperature comprises the instructions causing to: determine a secondtemperature of the diode array from the second incremental voltage and afirst slope of the incremental voltage to temperature curve for thediode array; and determine the first incremental temperature as adifference between the second temperature and the first temperature.